The project has two distinct components: 1. A series of human/hamster hybrid cells have been isolated which contain human DNA exclusively in the form of a minichromosome. These minichromosomes contain between 1500 and 10,000 kb and include the centromere of human chromosome. 1. As a result they segregate in a completely stable fashion during mitosis. Cloned, human probes are available from the screening of a genomic library of one of these hybrids, and we also have several cloned human satellite probes from other laboratories. One goal will be to increase the number of cloned probes derived from the minichromosomes. A second goal will be to map such probes representing various satellite, alphoid and unique sequences to large restriction fragments from the minichromosomes. These will be generated with restriction enzymes having relatively rare recognition sites, ad then fractionated by pulsed field or field inversion gel electrophoresis (FIGE). A long range goal of these studies is to understand the features of a mammalian chromosome which make up the centromere and hence specify the assembly of the kinetochore at mitosis. 2. Another project seeks to understand the mechanism for postranscriptional regulation of the enzyme ornithine decarboxylase. We will construct a hybrid gene containing the 5' untranslated region of ODC mRNA attached to the translated portion of the firefly luciferase gene in a mammalian expression vector. The effect of polyamines on translation will be studied in vivo and in vitro.